1. Field of the Invention
The present invention relates to a process for preparing ether carboxylates. More particularly, the invention relates to a process comprising oxidizing an ethoxylated primary alcohol or alkylphenol having a terminal hydroxy group or a polyoxyethylene/polyoxypropylene block copolymer, with oxygen, in the presence of water and a palladium catalyst, to convert the terminal --CH.sub.2 OH group to a carboxyl group and simultaneously neutralizing the thus-formed carboxyl group with an alkali whereby to form an alkali salt of the carboxylic acid.
2. Description of the Prior Art
A process for oxidizing primary alcohols, in the presence of a noble metal catalyst, with an oxygen-containing gas is known, and this process is outlined on page 303, volume 2 of "Newer Methods of Preparative Organic Chemistry" (Academic Press, New York, 1963). In the process described in this literature reference, an expensive platinum catalyst is exclusively used in a large amount, and therefore, this process is not suitable for the oxidation of nonionic surface active agents which is an intended use of the present invention. Japanese Patent Application Laid-Open Specification No. 34122/73 discloses a process comprising oxidizing and neutralizing one or two terminal primary hydroxy groups of polyethylene glycol to form a mono- or dicarboxylic acid salt. Pt or Pd is used as a catalyst in this process and the amount of the catalyst is very large, such as 30 to 138% based on the polyethylene glycol. Further, a long time is required and the concentration of polyethylene glycol is lower than 10% as is seen in the Examples of this publication. Even under these preferred conditions, the conversion is not very high. Moreover, as will be apparent from Examples 3, 7 and 8 of this publication, the conversion is drastically lowered as the polyoxyethylene chain becomes longer. For example, when the reaction is carried out at 35.degree. C. in the presence of a 5%-Pt/carbon catalyst, 2% of the mono-salt and 98% of the di-salt are obtained from diethylene glycol under conditions wherein the catalyst amount is 30% and the reaction time is 7 hours, but when triethylene glycol is used, 71.8% of the mono-salt and 20.5% of the di-salt are obtained by conducting the reaction for 9 hours. Moreover, in the case of polyethylene glycol 300, only 3.5% of the mono-salt and 7.5% of the di-salt are obtained by conducting the reaction for 5 hours. From the fact that when a 5%-Pd/carbon catalyst is used in an amount of 114% based on the diethylene glycol and the reaction is carried out for 7 hours, the product consists of 87% of the mono-salt and 12% of the di-salt (see Example 5), it is apparent that this 5-% Pd/carbon catalyst is not superior to a 5-% Pt/carbon catalyst. Accordingly, is cannot be expected from the teachings of this reference that a palladium catalyst can be used advantageously in industry for the oxidation of compounds having a polyoxyethylene chain in the molecule.